Friday, 1 October 2010

More Rendering of VectorMapDistrict Data

The nice people from Ordnance Survey have sent me a complete set of VectorMapDistrict data (which is on 6 DVDs!).   Surprisingly they didn't even charge me for the DVDs or postage.
Now I have all that data I thought I'd better do something with it!

First step was to get it onto a nice fast disk, so I copied it onto the hard disk of my server...which took a while...

Then I tried to use my vmdmap.py program to render it all, but mapnik bombed out with an error as it was adding the various shapefile layers.  I suspect that this is because every single shapefile is in its own layer, as it is a completely separate datasource, and I think I either ran out of memory or hit some mapnik internal limit.   This means I can't use vmdmap.py to render the whole country, which is a bit of a shame.

To get around this I think I need to merge them into a single datasource.  I don't know enough about manipulating shapefiles to do this, so instead am making use of shp2pgsql which allows you to import a shapefile into a postgresql database.   I have written another program, based on vmdmap.py called vmd2pgsql which will scan through a directory tree looking for the various shapefiles in the vectormap district dataset, and importing them into postgresql.   This gives a much lower number of tables - just one per shapefile name, but each one will have a lot of data.

It is importing now, so will see how long the import takes, then how well it renders.  I suppose it should render ok because I have the whole UK OSM dataset in a single database and that works, but we'll see over the weekend if it ever finishes!  The code is at my google code site.
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